My younger sister is no reason mature, but I'm more responsible?

Not too long ago, my mother said that my sister was more mature than I'm, despite me being the older brother. She looks for jobs and tries to keep herself busy. My mom also said that I'm more responsible, meaning that I can keep up with things I need to do or don't lose my belongings very much. There's a contrast with how my sister can handle situations calmly, while I tend to let my mind run with possibilities and freak out a little, but I can hold on to something for long periods of time. For example, when our house phone ringed to talk to my mother, I didn't know what to say, so my sister grabbed the phone and explained everything. Despite being mature my sister has a history of letting things get stolen, such as 4 phones (all of which are at least over $100 each, most recently she lost an iPhone that costs $200), her State ID, and a calculator I needed for a final exam one day prior because she placed those things on a desk in environments where other classmates have a reputation for stealing, while I have still held on to any important items like my phone, State ID, house keys, social security cards (which my mom had to hold for her because she loses things so much), and other belongings. This is why I'm hesitant to let her borrow my belongins, because almost every time I do, she loses them. This makes me wonder how exactly my mom views us as these. I always thought I was more mature, but apparently not in her eyes

There's a difference between responsible and mature. I'm sure your mom loves both of you the same.

Talk to her

You sound more mature than your sister, not sure why your mom can't see that